This invention relates to a wheel bearing device for supporting a wheel on an axle through tapered roller bearings.
Tapered roller bearings are bearings suited to bear radial load, axial load and their combined load. Due to their large load capacity, they are used to support axles of automobiles.
FIG. 5 shows an example of a wheel bearing device for a non-driven wheel of a truck. This wheel bearing device has a double-row tapered roller bearing 22 having a pair of inner rings 23 mounted on an axle 21. A hub 26 and a brake rotor 27 are fixed by bolts 28 to an outwardly extending flange 25 provided at one end of an outer ring 24. The inner rings 23 are prevented from coming out by a nut 29. A hub 26 carries wheel mounting bolts 30.
On the inner-periphery of the outer ring 24, two rows of raceways 31 are formed. Opposite the raceways 31, the pair of inner rings 23 are formed each with rows of raceways 32, respectively. Between these pairs of opposed raceways 31 and 32, a plurality of tapered rollers 33 are provided in two rows. The tapered rollers 33 roll with their large-diameter ends 34 abutting with flanges 35 provided at outer ends of the pair of inner rings 23, respectively.
Thus, the hub 26 and the brake rotor 27 fixed to the outer ring 24 are supported so as to be rotatable relative to the axle 21.
A contact type rubber seal 36 is provided at the inner end, that is, the end near the center of the axle 21, of an annular space in which the tapered rollers 33 are arranged in two rows. A cap 37 covers the outer end, i.e. the end near the end of the axle 21 together with the end of the axle on which is mounted the nut 29 to prevent scattering of lubricating grease in the bearing and entry of dust and water from outside.
The bearing portion of such a wheel bearing device as described above is periodically greased and maintained. With increasing horsepower and loading capacity of modern cars, higher resistance to high loading and high temperature during high-speed cruising are required for wheel bearing devices. Long-term maintenance-freedom is also desired. Under high-load, high-temperature conditions, grease sealed in the bearing portion of a wheel bearing device tends to deteriorate quickly. Thus a highly heat-resistant, long-life grease is desired. Also, it is required to maintain long life of bearing members under high-load, high-temperature conditions.
As mentioned above, since tapered rollers of a tapered roller bearing roll with their large-diameter ends abutting with the flanges of the inner rings, heat is produced at the sliding portions between the roller ends and the flanges. The higher the load, the higher the contact pressure between the roller ends and the flange, and thus the greater the heat produced.
Heretofore, for the inner circumferential surface shape of the outer ring 24, the portion between the pair of raceways 31 was made straight and no measure for reducing weight has been taken. Also, one of the factors that influence the bearing life is whether the lubricating condition is good or bad. The amount of lubricating grease sealed depends on the volume of the internal space of the bearing. But heretofore, it was not structured taking into account the amount of sealed grease, so that there was a limit on the amount of grease.
An object of this invention is to provide a wheel bearing device which assures long life even under high-load, high-temperature conditions.
Another object of this invention is to reduce the weight of a wheel bearing device for an axle and to increase its life.